Rich, potent vintage or tawny port will take the chill away

In wine, freezing temperatures mean it’s time for port, a fortified wine made from grapes grown in Portugal’s Duoro River Valley. Port starts life like any red wine: Up to five kinds of red grapes are harvested and crushed, sometimes still by foot, which allows the sugar-laden juice to come in contact with yeast so fermentation can begin.

After three days, the winemaker adds brandy, which raises the alcohol to 20 percent (hence, the term ”fortified”) and kills the yeast, stopping fermentation before all the grape sugar has been converted to alcohol. The resulting wine has an engaging combination of fire and sweetness. The wines are shipped down the Duoro River to Oporto (which explains the origin of the name port), where they are aged.

Drinking vintage port, which captures the limelight but accounts for only about 2 percent of the region’s production, is an exercise in serious devotion. A bottle needs 20 or more years of aging in a cool cellar and careful decanting to rid it of the sediment, accumulated from aging, before serving. And, despite the practice in restaurants of offering a glass of vintage port from a bottle that has been opened for weeks, vintage port, like all fine wine, deteriorates rapidly after opening. A bottle should be consumed in one or, at most, two evenings, which, given its alcohol content, means you need a large gathering.

Enter aged tawny port. Aged in barrels for 10 to 40 years after it’s made, tawny port takes on a brown-brick hue (hence, its name) with flavors of nuts, caramel, and dried fruits on top of the sweetness and fire. It has left its sediment in the barrel so decanting is not necessary. Since it has been exposed to air for years while in the barrel, a little more won’t hurt it. You can have a glass, recork the bottle, and enjoy another glass a week or a month later.

W.J. Graham is one of the great port houses. It produces exquisite vintage ports and sublime aged tawny ports. Its 10-year-old tawny (about $28) has remarkable complexity and its 20-year-old (about $50) is gloriously rich. A glass of either after dinner will help dissipate winter’s chill.